Using an established colony of clinically normal inbred dogs all of whom have the serological abnormalities of systemic lupus erythematosus (SLE), it has been found that cell free extracts of their spleens could transmit these serological abnormalities to mice. These mice also developed lymphomas in which an infectious murine leukemia virus has been identified. Studies are in progress to isolate and characterize the canine agent responsible for these effects in mice. Studies are also in progress to determine the relation, if any, between the virus isolated from the murine lymphomas and SLE in humans and dogs.